Effect of post-heat treatment on the microstructural, mechanical, and bioactivity behavior of the microwave-assisted alumina-reinforced hydroxyapatite cladding

Abstract

The current research involves using microwave energy to modify the surface layer of UNS S31254 stainless steel in order to improve its bioactivity by cladding it with alumina-reinforced hydroxyapatite. For the microwave surface modification process, an industrial microwave oven supported by an infrared pyrometer and functioned at 1.1 kW and 2.45 GHz was utilized. In addition, the surface-modified samples were thermally heat-treated in a muffle furnace for 1 h at three different temperatures 400°C, 600°C, and 800°C. Scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffractometer, and simulated bodily fluid testing were used to investigate the metallographic, compositional, phase analysis, and bioactivity of microwave surface-modified samples. The presence of alumina in the microwave surface-modified samples was confirmed by X-ray diffractometer analysis. The microwave-assisted surface modification layer contains predominantly iron (Ni-Fe)-based austenite dendrites, as well as hydroxyapatite and certain reaction products, mostly in the interdendritic areas, according to the microstructural analysis. The results indicate that the heat-treated surface-modified samples exhibit lower porosity and higher hardness than the as-deposited surface-modified samples. Furthermore, the 800°C heat-treated samples exhibited the lowest porosity (about 56% less than that of the as-deposited sample) and maximum hardness (about 23.5% more than the as-deposited sample) among all the heat-treated samples. The bone binding ability of the surface-modified samples was decreased after heat treatment due to the reduction of pores and amorphous phase after the heat treatment process.